The total installed capacity for solar photovoltaics (PVs) has been increasing dramatically in the past few years because of price drop, government subsidies, as well as increased consumer awareness of environmental issues. Rapid power and voltage fluctuations along distribution feeders caused by behind-meter PVs have created serious operational issues such as overvoltage, reverse power flow, flickers, and equipment overloading. Energy storage devices (ESDs) can store energy for future use, smooth out large power fluctuations, and provide reactive power support to stabilize system voltage, making them one of the most effective technical solutions for the aforementioned operational issues. However, ESDs are expensive. Comprehensive cost-benefit studies have shown that the following strategies may make using ESDs more cost-effective: 1) providing multiple services to increase the utilization rate and revenue streams, 2) using demand-side management (DSM) to reduce the size of ESDs, and 3) sharing ESDs among a group of users to reduce the amount of ESD needed at the aggregated level.
Previous studies on sizing ESDs based on technical requirements focused mainly on smoothing power outputs of large solar or wind farms as described in P. Denhol, E. Ela, B. Kirby, and M. Milligan, the role of energy storage with renewable electricity generation, vols. NREL/TP-6A2-47187, January 2010. ESDs sizing studies at the residential level have not been fully investigated. Also, the previous studies only use worst case or average case to do the sizing study.
At residential households, communities, and feeders, level-sizing considerations may vary according to the ownership, location, and service requirements of an energy storage system. For example, an ESD on a residential feeder can be owned by: 1) a homeowner for supporting the rooftop PV system, 2) a utility for power quality and reliability considerations, or 3) a third-party aggregator for providing grid services. A home-owned ESD is behind-the-meter for balancing the home's own consumption needs. A utility-owned ESD may be placed close to a transformer or provides feeder-level services that impact all users on the feeder. Third party-owned ESDs may be placed on separate sites or even on mobile trucks for providing services to whoever needs them.
Another technical challenge for the residential ESD sizing study is the modeling of residential load consumptions. A typically approach is to use hourly average- or worst-case load profile derived from historical data for sizing ESDs. A major disadvantage of the approach is that it cannot account for the load pattern shift caused by behavioral changes of residential customers after the PV is installed. In addition, because both the PV generation and residential load consumptions are highly intermittent, considering a wider range of operation conditions is needed to size an energy storage system so that the performance of the ESDs will meet the requirements within a given risk margin.
Accordingly, what is needed, as recognized by the present inventors, is a method and a system for sizing ESDs for residential households, communities, and feeders.
The foregoing “Background” description is for the purpose of generally presenting the context of the disclosure. Work of the inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.